Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats


7*4

Gauge Notches.
TABLE OF COEFFICIENTS (average value).

Orifice is C
	Sharp-edged.
	Reentrant.
	Cylindrical.
	Bell-mouthed.

	'97
	I
	•82
	'99

P
	'0628
	o
	"5
	*O2

K.
	-64
	'53
	i
	i

C
	•62
	'53
	•82
	*99

Measurement of Stream Horse-Power by Gauge
Notches.—Let a stream be partly dammed, the water flowing
through the rectangular notch, abed, Fig. 699. To find the
discharge, divide H into very small portions h, and treat every
small rectangle as a separate orifice, whose area will, when ^ is
infinitely small, be shewn by B, At any depth Ha, # = S^/Hp
l%d discharge through small rectangle = 8 B A/H^. Shewing the
various discharges by horizontal lines on base ef, the figure is a
parabola (the lines a N/H^, whose base is 8 B \/H. Then

Theoretical      ^

cub. ft. per sec.    J

Actual discharge Qa = 5\ C H B JH
where C, the co-efficient of discharge

= '57 4- {breadth of notch -~ (10 x breadth of weir)}

Prof. Jaines Thomson adopted the triangular notch A, where
B/H is constant throughout, suspecting that C would be thereby
regular; and he found that Q a Hf. Taking an apex angle
of 90°,

Qa per sec. == 2-635

where C
notch,

Horse Rower I
of Stream   j

•617 (included in coefficient 2*635).   Finally, for any

( available

foot pounds per sec. x 60     Q G
__                  __

„ ) height of

* 1   faUin

I    feet.